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POUpdating database record using Entity Framework (lazy loading and virtual properties)
 

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  1. POUpdating database record using Entity Framework (lazy loading and virtual properties)
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    <p>I'm struggling with <em>updating</em> existing lecturer's data in database. <br /> Every lecturer has <strong>Name</strong>, <strong>AcademicDegree</strong> and <strong>Courses</strong> which are taught by him/her (<em>Courses==Lessons</em>). </p> <p>In fact there are more properties in <code>class Lecturer</code> but they are not relevant. For simplicity lets assume that <a href="http://en.wikipedia.org/wiki/Plain_Old_CLR_Object" rel="nofollow noreferrer">POCO</a> class is defined this way:</p> <pre class="lang-cs prettyprint-override"><code>// POCO class (Entity Framework Reverse Engineering Code First) public class Lecturer { public Lecturer() { this.Courses = new List&lt;Course&gt;(); } public int Id_Lecturer { get; set; } // Primary Key public string Name { get; set; } public int? Academic_Degree_Id { get; set; } public virtual AcademicDegree AcademicDegree { get; set; } public virtual ICollection&lt;Course&gt; Courses { get; set; } } </code></pre> <p>In <em>Data Access Layer</em> I have method <code>void UpdateLecturer(Lecturer lecturer)</code> which should update lecturer whose <code>Id_Lecturer</code> is equal to <code>lecturer.Id_Lecturer</code> (using <code>lecturer.Name</code>, <code>lecturer.AcademicDegree</code> and <code>lecturer.Courses</code>). </p> <p>It's very handy method because in <em>ViewModel</em> I can call <code>_dataAccess.UpdateLecturer(SelectedLecturer)</code> (where <code>SelectedLecturer</code> is binded in <a href="http://en.wikipedia.org/wiki/Extensible_Application_Markup_Language" rel="nofollow noreferrer">XAML</a>; <code>SelectedLecturer</code> properties can be set by user in <code>TextBox</code>es and <code>Checkbox</code>).</p> <p>Unfortunatelly this method:</p> <pre class="lang-cs prettyprint-override"><code> public void UpdateLecturer(Lecturer lecturer) { using(var db = new AcademicTimetableDbContext()) { // Find lecturer with Primary Key set to 'lecturer.Id_Lecturer': var lect = db.Lecturers.Find(lecturer.Id_Lecturer); // If not found: if (lect == null) return; // Copy all possible properties: db.Entry(lect).CurrentValues.SetValues(lecturer); // Everything was copied except 'Courses'. Why?! // I tried to add this, but it doesn't help: // var stateMgr = (db as IObjectContextAdapter).ObjectContext.ObjectStateManager; // var stateEntry = stateMgr.GetObjectStateEntry(lect); // stateEntry.SetModified(); db.SaveChanges(); } } </code></pre> <p>updates everything (i.e. <code>Id_Lecturer</code>, <code>Name</code>, <code>Academic_Degree_Id</code> and <code>AcademicDegree</code>) <strong>except</strong> <code>Courses</code> which are unchanged after <code>db.SaveChanges()</code>. </p> <p>Why? How can I fix it?</p> <hr> <p>Similar problems: </p> <ul> <li><a href="https://stackoverflow.com/questions/6655716/updating-an-entity-in-entity-framework">updating-an-entity-in-entity-framework</a></li> <li><a href="https://stackoverflow.com/questions/700192/how-do-can-i-attach-a-entity-framework-object-that-isnt-from-the-database">how-do-can-i-attach-a-entity-framework-object-that-isnt-from-the-database</a></li> <li><a href="http://blogs.msdn.com/b/adonet/archive/2011/01/29/using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx" rel="nofollow noreferrer">using-dbcontext-in-ef-feature-ctp5-part-4-add-attach-and-entity-states.aspx</a></li> <li><a href="https://stackoverflow.com/questions/1612655/entity-framework-updating-with-related-entity">entity-framework-updating-with-related-entity</a></li> <li><a href="https://stackoverflow.com/questions/4168073/entity-framework-code-first-no-detach-method-on-dbcontext">entity-framework-code-first-no-detach-method-on-dbcontext</a></li> </ul> <hr> <p><em>-- Edit --</em></p> <p>I also tried this way (idea came from <a href="https://stackoverflow.com/questions/12585664/an-object-with-the-same-key-already-exists-in-the-objectstatemanager-the-object#12587752">this post</a>): </p> <pre class="lang-cs prettyprint-override"><code>public void UpdateLecturer(Lecturer lecturer) { using (var db = new AcademicTimetableDbContext()) { if (lecturer == null) return; DbEntityEntry&lt;Lecturer&gt; entry = db.Entry(lecturer); if (entry.State == EntityState.Detached) { Lecturer attachedEntity = db.Set&lt;Lecturer&gt;().Find(lecturer.Id_Lecturer); if (attachedEntity == null) entry.State = EntityState.Modified; else db.Entry(attachedEntity).CurrentValues.SetValues(lecturer); } db.SaveChanges(); } } </code></pre> <p>but still <em>Courses</em> don't overwrite old values.</p> <hr> <p>-- Edit 2 --</p> <p>In response to the @Slauma question I'll describe how I loaded <code>SelectedLecturer</code> (which is passed to <code>UpdateLecturer(Lecturer lecturer)</code> method as an argument). </p> <p>I'm implementing <a href="http://en.wikipedia.org/wiki/Model_View_ViewModel" rel="nofollow noreferrer">MVVM</a> concept so I have <em>View</em> project within my <em>Solution</em> with <code>DataContext</code> set to <code>LecturerListViewModel</code>. In <em>View</em> there is <code>DataGrid</code> with list of all lecturers fetched from databse. <code>DataGrid</code> is binded this way: </p> <pre class="lang-xml prettyprint-override"><code>&lt;DataGrid AutoGenerateColumns="False" Name="LecturersDataGrid" HeadersVisibility="Column" IsReadOnly="True" ItemsSource="{Binding Lecturers,Mode=TwoWay}" SelectedItem="{Binding SelectedLecturer, Mode=TwoWay}"&gt; &lt;DataGrid.Columns&gt; &lt;DataGridTextColumn Header="Name" Binding="{Binding Name}" /&gt; &lt;DataGridTextColumn Header="Academic degree" Binding="{Binding AcademicDegree.Degree_Name}" /&gt; &lt;DataGridTemplateColumn&gt; &lt;DataGridTemplateColumn.CellTemplate&gt; &lt;DataTemplate&gt; &lt;StackPanel Orientation="Horizontal"&gt; &lt;Button Content="Edit" Click="EditButtonClick"/&gt; &lt;Button Content="Delete" Command="{Binding DataContext.RemoveLecturer, ElementName=LecturersDataGrid}" /&gt; &lt;/StackPanel&gt; &lt;/DataTemplate&gt; &lt;/DataGridTemplateColumn.CellTemplate&gt; &lt;/DataGridTemplateColumn&gt; &lt;/DataGrid.Columns&gt; &lt;/DataGrid&gt; </code></pre> <p><code>Lecturers</code> are fetched from database in <code>LecturerListViewModel</code> constructor in this way: </p> <pre class="lang-cs prettyprint-override"><code>/// /// Code within LecturerListViewModel class: /// // All lecturers from database. public ObservableCollection&lt;Lecturer&gt; Lecturers // Constructor public LecturerListViewModel() { // Call to Data Access Layer: Lecturers = new ObservableCollection&lt;Lecturer&gt;(_dataAccess.GetAllLecturers()); // Some other stuff here... } private Lecturer _selectedLecturer; // Currently selected row with lecturer. public Lecturer SelectedLecturer { get { return _selectedLecturer; } set { SetProperty(out _selectedLecturer, value, x =&gt; x.SelectedLecturer); } } /// /// Data Access Layer (within DataAccess class): /// public IEnumerable&lt;Lecturer&gt; GetAllLecturers() { using (var dbb = new AcademicTimetableDbContext()) { var query = from b in dbb.Lecturers.Include(l =&gt; l.AcademicDegree).Include(l =&gt; l.Timetables).Include(l =&gt; l.Courses) select b; return query.ToList(); } } </code></pre>
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